<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>绝对定位练习</title>
    <style>
       div{
           width: 300px;
           background-color: rgba(0,0,0,0.3);
           padding: 10px;
           position: relative; /*相对定位*/
       }
       input{
           width: 260px;
            border: 0; /*去掉自带边框*/
           padding: 10px 20px;
       }
       img{
           position: absolute; /*绝对定位*/
           top: 14px;
           right: 30px;
       }
       p{
           font-size: 12px;
           color: red;
           margin: 0;
       }

    </style>
</head>
<body>
<div>
    <input type="text" placeholder="请输入用户名">
    <img src="http://doc.canglaoshi.org/tstore_v1/images/login/yhm.png" alt="">
    <p>用户名不能为空</p>
</div>
</body>
</html>